This disclosure sets out a method and apparatus for obtaining formation fluid delivered into a wireline supported formation test tool, and in particular a test tool which is able to perform segregated testing. That is, it achieves the goal of obtaining a fluid sample from the connate formation fluids and avoids mixtures with drilling mud filtrate. This is particularly useful in making test identification prior to sample collection.
Existing formation testers have a limited fluid storage capacity. They include typically two or three fluid collection tanks or chambers in them. Heretofore, attempts to obtain connate formation fluid have been implemented by first and second separated tests. The first test obtains a first sample which is more likely to be contaminated with filtrate from the drilling mud. It will be recalled that this type testing is normally carried out in open hole where the side wall of the borehole is covered by a mud cake. The mud cake is formed by separation of the mud into the mud cake and filtrate which penetrates many of the formations of interest. That is, the formation absorbs a portion of the drilling mud. The typical testing procedure involves the extension of a test probe against the side wall. It has a seal ring to perfect a seal so that the region adjacent the test probe is not eroded. Moreover, a snorkel is normally extended through the center of the seal to assure that the tip of the snorkel is drawing fluid from the formation at the depth of penetration. This may obtain the connate formation fluid, but always, there is the risk that filtrate will penetrate to that depth. In fact, some formations are able to accept filtrate for substantial depths into the formation. In any event, the filtrate may commingle with formation fluid and the first sample removed might be contaminated with the filtrate. Segregated tests have been performed in the past where a first sample is taken and stored in a first container or tank within the test tool, and then a second sample is taken and also stored but it is stored in a separate tank. If filtrate penetration into the formation is not excessive, the second sample may be sufficiently pure to represent fairly the connate fluid from the formation. Additional tests are difficult to implement. At most, only three containers can be typically included in the formation test tool. Where several test chambers must be filled, this then requires retrieval of the tool to empty the test chambers so that subsequent tests can be made. This also regrettably requires a return trip to the surface. Multiple trips can be used to perform multiple tests at a given formation, but it is hard to locate the test tool at the requisite horizons in multiple trips. Accordingly, segregated testing involves multiple trips of the test tool and it is not a good solution.
The present disclosure sets out an apparatus and a method of operation whereby a sample is taken from the formation and is tested to assure that invasion fluid did not commingle with the sample, and that the sample is the connate fluid from the formation. The present apparatus utilizes first and second separate test probes with separate snorkels, and they are arranged diametrically opposite one another. With one, a fluid sample can be taken from a formation, and with the other, a portion or all can be reinjected into the formation. The fluid sample is forced through the tool from the inlet snorkel so that the sample can be tested. The type of testing is variable; typically it can be tested for sound transmission, magnetic wave transmission, conductivity, or other factors. The test selected determines the presence of constituents known to be in the well fluids so that their absence substantially indicates greater recovery of connate formation fluids. To this end, the device can include sample storage containers or tanks. Testing devices are included also. Testing devices are connected between the separate snorkels which serve as inlet and outlet. The testing devices test recovered fluid as it is pumped through the tool. Once it is determined that the formation fluid has not been invaded, a valving system is operated so that storage tanks or containers in the tool can be filled. A pump is included so that fluid recovered from the inlet snorkel is directed through the tool and to the outlet snorkel for restoration to the formation.